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Loading same dll more than once in a Java JVM

Arun SanbhatAug 23 2018 — edited Aug 24 2018

Hi,

We are currently using Java JRE 1.8 u 131 on WINDOWS. We have a java standalone desktop application that loads a C dll for processing of data.This it does by loading the dll using System.LoadLibrary("Name of the dll") function call.

Currently the Java application is single threaded and is processing the data using JNI functions written in C classes inside the dll.

Due to increase in the data by many folds, we would want to make the java application multi-threaded. The C side code does not support multi-threading and cannot be changed due to legacy issues. So we plan to use Java multithreading feature and load the same dll in each thread.

Each thread should process the data separately. However I am not sure if this will work. Can someone please inform me if a dll when loaded by any one of the Java threads, can other thread also be able to load it again? Will the dll would be loaded in a single memory space in the JVM or can each dll will be allocated a separate memory that can be only be accessed by the thread that has loaded it?

Comments

Mike Kutz

bitmap
Bitmap indexes implies Serialization. That's like having the db parameter _SLOW=TRUE.
It can speed up SELECTS, but at a cost for other DML operations.
In my uses, it's not about the "low cardinality" of the answers in a column, but the "low cardinality" of your query results.
Eg finding out that a particular song, sung by Adam Sandler about Tinder results for other Eskimos in his tribe, is true
I've used them to speed up ad hoc queries on final reporting tables.
Billy uses them to show you can count 42B rows in under 1s.
Partition
"Prevent FTS" is one use for Partitions.
The primary use I've seen is for data management.
Need to remove 1 mo worth of data? Drop a Partition
Also, research ILM in the Data warehouse guide. This helps automate the task of moving chunks of old data for you. (Eg move 1mo worth of 3yr old data from tablespace on SSD to compressed read-only tablespace on SATA)

User_JNHXJ

Thank for replying mike
i have a couple of question
1.what u mean by ad hoc query is query using bind variable in where clause? or is there a different meaning?(from what i know ad hoc query is a type of query where result set is depent on the value supplied to a variable)

2."Need to remove 1 mo worth of data? Drop a Partition" even if we drop a partition the actual table still have the data from that partition right? and for what purpose we dropping this data? for memory or just deleting old data?

Mike Kutz

Ad hoc
This is what most end users want to perform.
APEX IR searches are ad hoc queries. Especially those faceted searches.
Bitmap indexes could drastically improve multi-column queries of these types even on a 1 B row table.
But, INSERT/UPDATE/DELETES would be horrible. You'll want to do infrequent bulk operations from a single transaction only. Tools like DBMS_PARALLEL_EXECUTE will cause the crud operation to take longer if parallel_level is higher than 1. (I learned this the hard way)
Drop Partition
You usually remove old data for legal reasons.
Partitions are individuals tables magically joined together to act as 1 table. If you read the history of Oracle, Partitions started in v7.3 as Partitioned VIEWs.
So, when you DROP a Partition, you are actually dropping a table.
Which then brings up Partition EXCHANGE. In this case you are actually swapping one table for another. And because the DD is only swapping the pointers, this is extremely fast.
You can swap in/out a table's worth of data in the blink of an eye. (I'm ignoring INDEXES)
Again, I find Partitions more useful for data management. But queries performance shouldn't be ignored.

User_JNHXJ

thanks for the partition part i got a little insigth about it.
but still have question about bitmap
can you explain example of "faceted searches" is it like result set with low cardinality?(FYI first time hear faceted word so i do not understand)

Mike Kutz

Faceted Search example using APEX.

https://blogs.oracle.com/apex/post/apex-192-faceted-search

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